Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Related Articles


Fire Flow Test w Pitot Pressure

Fire Flow Test w Pitot Pressure

Fire Flow Test w Pitot Pressure

Its been a while for me but for fire flows in the past I was used to receiving my static pressure, flow and residual pressure. I would then either graphically or mathematically would utilize these numbers to predict how the system performed to say either at minimum pressure of 25 or 20 psi.

I've received a flow test that includes a Static of 44 psi, residual pressure of 25 psi and a pitot pressure of 11 psi.

Using Q = 29.83 x c x d^2 x p^0.5 I'm arriving at 556 gpm as the flow (assuming c=0.9 and d=2.5 inches)

This gets me the flow of 556 gpm with a residual pressure of 25 psi.

Projecting this using your typical logarithmic graph for water flow and pressure, this results in about 630 gpm when the pressure goes down to 20 psi in the system.

Am I approaching this correctly? In short, I'm using the pitot pressure to arrive at my residual flow. In other words the pitot pressure is not necessarily the same as the system residual pressure.

Please advice,

RE: Fire Flow Test w Pitot Pressure

I think you are using the data correctly, but those are some sad system numbers if you're trying to achieve any sort of fire flow.


RE: Fire Flow Test w Pitot Pressure

Thanks Pinwards

Yes, agree. Luckily there appears to be a newer and separate larger line which is exhibiting larger flows, in the order of 1750 gpm at 20 psi residual. So trying to clarify how older hydrants and the newer line are related by testing at different points. The data I provided was only for one of the three hydrants tested in the vicinity.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close